Mr Cameron and Mr Osborne were initially attracted to the idea of building a hub airport with four runways in the Thames estuary. Photo: Wikipedia

Mr Cameron left open the prospect that the Conservatives would campaign at the 2015 election in favour of expanding Heathrow – a move that would please the business lobby but infuriate environmentalists and Londoners living under the flight path.

Although the coalition deal with the Liberal Democrats excludes building another runway at Heathrow, the prime minister believes there is an urgent need to develop London’s air links with emerging markets.

Questioned in the Commons, Mr Cameron refused to rule out a change of heart. While restating the coalition’s position, he said: “We must not be blind to two important considerations: how we expand airport capacity overall and how we ensure Heathrow operates better.”

Government insiders confirmed that both Mr Cameron and George Osborne, the chancellor, had an open mind on expanding Heathrow, although any change of policy would not come before the election.

Zac Goldsmith, the environmentalist and Tory MP for Richmond Park, said that up to 2m people living under the flight path – including his constituents – would resist a new runway, adding: “I could not stand on a Conservative platform that included an expansion of Heathrow.”

Mr Cameron and Mr Osborne were initially attracted to the idea of building a hub airport with four runways in the Thames estuary. But their enthusiasm has waned as details have emerged on…..